The most revealing parts of polls are often not the voting intention figures, which get the headlines, but other answers that explain what is happening to the underlying attitudes of voters. These can identify deeper shifts and suggest whether a big lead is likely to be sustained over time.

The latest Populus poll for The Times is unremittingly awful for Gordon Brown. There has been a collapse of confidence in his leadership, particularly among Labour voters, who want him to step down. But how well are David Cameron and the Tories doing? Their 40 to 29 per cent edge over Labour is the biggest in a Populus poll, but this is only part of the story.

More significant are two other questions. First, Mr Cameron’s leader rating (on a 0 to 10 scale) has risen over the past month from 4.96 to 5.36. This is the highest since Mr Cameron took over in December 2005 and makes him the most popular Conservative leader since Populus started asking this question more than five years ago. Moreover, his rating has risen sharply among Tory voters since early April, from 6.32 to 7.03, well above the other leaders’ ratings with their own voters.

Secondly, the Tories are winning the battle of economic competence. The number trusting Mr Brown and Alistair Darling to deal with economic problems in the best interests of Britain has plummeted since early September after the Northern Rock, credit crunch and 10p tax rows: from 61 per cent down to 30 per cent. Mr Cameron and George Osborne did not benefit at first, but they have advanced recently from 27 per cent last September to 40 per cent now as most trusted.

These are potentially crucial shifts that underpin movements in voting intentions. If Labour is no longer trusted more than the Tories on the economy, it is hard to see how the party can win the next election. Evidence that the economy has turned is a long way off, but Mr Brown no longer has the reserves of political support with the necessary patience.

There is also the complication for Mr Cameron of the Liberal Democrats, who refuse to be squeezed out of the race at 19 per cent, up two points over the month. Their estimated national share of the vote fell last Thursday, but they achieved a net gain of seats, winning from Labour in the North and losing to the Tories in the South. This has boosted Nick Clegg, whose leader rating has risen for the second month running, up from 4.27 to 4.52 among all voters and from 5.53 to 5.72 among Lib Dem supporters.

Yet if voters are warming to Mr Cameron and the Tories, the story of the past week was essentially about the unpopularity of Mr Brown and Labour. The Tories need a firmer base if they are to win outright rather than merely deny Labour an absolute majority. As the Cameron camp accepts, the Tories have to do much more to give the public a reason to vote for them rather than against Labour.

Populus interviewed a random sample of 1,509 adults aged over 18 by telephone between May 2 and 4. Interviews were conducted across the country and have been weighted to be representative of all adults. Populus is a member of the British Polling Council.

For more details go to www.populus.co.uk.

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